1. Field of the Invention
The present invention relates to an optical switch configured by connecting multiple stages of optical switching elements each of which switches an optical transmission channel.
2. Description of the Related Art
As an example of a conventional optical switch, there is an optical switch that is described in Japanese Patent Application Laid-open No. 2004-246302. The optical switch is configured to avoid destroying an optical signal that is conducting when switching the output destination of an optical signal, and to output the optical signal to each of optical waveguides before and after the switching while switching the output destination.
However, according to an optical-switch switching-control circuit disclosed in the paten document No. 2004-246302, it is considered to avoid destroying an optical signal that is conducting; but cannot avoid crosstalk that an optical signal temporarily interferences into a switching channel that is irrelevant to switching at the moment of the switching. As a result, where the above conventional optical switch is applied to switching of the transmission channel of an optical communication signal and when crosstalk occurs at the moment of the switching, there is a problem such that an optical communication signal under the switching is leaked into a switching channel irrelevant to the switching, and confidentiality of communication contents cannot be maintained.
Moreover, there is another problem that when a switching channel irrelevant to the switching is coupled downstream of the switching to another optical transmission channel in operation by using an optical coupler, crosstalk light destroys an optical signal in the optical transmission channel in operation, and causes a communication trouble.
The present invention has been made in the light of the above, and an object of the present invention is to obtain an optical switch and an optical-switch control method according to which crosstalk dose not occur when switching an optical transmission channel.